1. Field of the Invention
The present invention relates to data communication techniques and particularly to communication apparatuses that constitute a ring network, to interface cards to be installed in the communication apparatuses, and to a failure handling method performed by the communication apparatuses.
2. Description of the Related Art
As a highly-reliable communication network, a communication network in which multiple communication apparatuses that relay a data frame are connected in a ring shape, that is, a so-called ring network is often built. Data frame looping needs to be prevented in a ring network. Thus, by using a protocol for ring control (hereinafter, referred to as a “ring protocol”), at least one port of a communication apparatus is often set as a port that blocks the relay of a data frame (hereinafter, referred to as a “block point”).
Upon the generation of a failure in the communication line between communication apparatuses, the setting position of a block point is dynamically changed based on the ring protocol so that a data frame is not transmitted to the communication line where the failure has been generated. This allows for the data frame transmission to be continued by bypassing the communication line where the failure has been generated.    [Patent document 1] Japanese Laid-Open Publication No. 2006-229477
Conventional ring protocols are directed to maintain the transmission of data frames when a failure is generated in the communication lines among communication apparatuses. The transmission of the data frames is not sometimes able to be maintained when a failure is generated inside the communication apparatuses.